Noroviruses (also known as Norwalk-like viruses or Norwalk viruses) and Sapoviruses (also known as Sapporo-like viruses) are etiological agents of acute gastroenteritis in adults and children (Green et al. J. Infect. Dis. 181 (Suppl 2):S322-330). Norviruses and Sapoviruses are members of the Caliciviridae family of small, nonenveloped viruses, 27-35 nm in diameter, containing a single-strand of positive-sense genomic RNA. Currently, Norviruses and Sapoviruses are the only two genera of the Caliciviridae family known to cause human disease.
Noroviruses cause greater than 90% of nonbacterial gastroenteritis outbreaks and an estimated 23 million cases of gastroenteritis in the U.S. per year (Fankhauser et al. (2002) J. Infect. Dis. 186:1-7; MMWR Morb. Mortal Weekly Rep. (2000) 49:207-211). Although, the Norwalk strain of Norovirus was the first discovered, it is now apparent that the Norwalk virus causes less than 10% of gastroenteritis cases, whereas other members of the Norovirus family, such as the Lordsdale virus, Toronto virus, and Snow Mountain virus, may cause 90% of cases (Fankhauser et al. (1998) J. Infect. Dis. 178:1571-1578; Nishida et al. (2003) Appl. Environ. Microbiol. 69(10):5782-6).
The symptoms of Norovirus infection include simultaneous diarrhea and vomiting as well as fever, headaches, chills and stomach-aches. The cause of such symptoms may be related to the binding of Noroviruses to carbohydrate receptors of intestinal epithelial cells, which results in an imbalance in ion transfer (Marionneau et al. (2002) Gastroenterology 122:1967-1977; Hutson et al. (2003) J. Virol. 77:405-415). Extremely contagious, Noroviruses can cause disease by infection with as few as 10 virions. Although, otherwise healthy people infected with Noroviruses may recover within 2-4 days, they may still shed virus for up to 2 weeks after the onset of symptoms; hence, infected individuals should be quarantined for up to two weeks. Approximately 30-40% of infected people may remain symptom-free, though spread infection by shedding of virus to others who may be more susceptible to infection (Hutson et al. Trends Microbiol. 2004 Jun; 12(6):279-287).
In contrast, Sapoviruses are less prevalent in gastroenteritis outbreaks and infect mostly infants and children, though occasionally adults (Zintz et al. (2005) Infect. Genet. Evol. 5:281-290; Johansson et al. (2005) Scand. J. Infect. Dis. 37:200-204; Rockx et al. (2002) Clin. Infect. Dis. 35:246-253). Sapoviruses also cause diarrhea and vomiting and spread infection through viral shedding, which may last for up to 2 weeks.
There remains a need for an improved therapy for treating patients having gastroenteritis associated with Norovirus or Sapovirus infection and methods for preventing the spread of infection.